Method and apparatus for manufacturing articles of bonded granules



R. C. BENNER ET AL May 28, 1935.

METHOD AND APPARATUS FOR MANUFACTURING ARTICLES OF BONDED GRANULESOriginal Filed Feb. 13, 1933 3 SheetsSheet 1 INVENTORS May 28, 1935. R.c. BENNER ET AL 2,003,131

METHOD AND APPARATUS FOR MANUFACTURING ARTICLES 0F BONDED GRANULESOriginal Filed Feb. 13, 1933 5 Sheets-Sheet 2 Mm. Pans Mm. 61mm MAXP0175 MIN. 67mm! MA/r Pan E Mm. 61mm MAX. GRAIN MIN. PORL' f 5 MAX/MUMP005 (1 MIN/MUM 6mm MAX. P0175 Mm. PURE INVENTORS May 28, 1935. R. c.BENNER El AL 2,003,131

METHOD AND APPARATUS FOR MANUFACTURING ARTICLES OF BONDED GRANULESOriginal Filed Feb. 15, 1935 5 Sheets-Sheet 3 xv: ii! ill}. 1

INVEITTORS C. 7'- rvwzrn TON Patented May 28, 1935 UNITED STATES PATENTOFFICE METHOD AND APPARATUS FOR MANUFAC- TURING ARTICLES OF BONDED GRAN-ULES Original application February 13, 1933, Serial No. 656,500. Dividedand this application December 14, 1933, Serial No. 702,332

21 Claims.

This invention relates to the manufacture of articles formed of bondedparticles, such as abrasive and refractory wheels and shapes. Moreparticularly, our invention is concerned with the manufacture ofarticles of an abrasive or ceramic nature, according to which adifferent relation of the particles and the bond therefor is obtained inthe resulting articles than has heretofore been obtainable, andaccording to which articles of this nature having a considerablysuperior character are produced.

This application is a continuation in-part of our earlier filedapplication Serial No. 245,659, filed January 10, 1928, and is adivision of .our copending application Serial No. 656,500, filedFebruary 13, 1933. p

The invention will hereinafter be described with reference to themanufacture of abrasive articles, particularly abrasive wheels, but thisis by way of illustration, and it will be understood that the inventionapplies equally to the manufacture of articles of a ceramic nature,whether intended for abrasive purposes or not, and where the particulardisposition ofthe bond with reference to the individual particles is ofthe peculiar character sought to be obtained with the present invention.

Heretofore there have been two pricipal methods in use for the formingof abrasive and refractory articles. One of these (called the puddleprocess) employs a very wet mixture or slip comprizing approximately 20%of water. The other process is known by various names according to themethod used in applying pressure, and consists in the molding underpressure of a damp mix containing only about 2.5% of water.

The present invention pertains to that method in which a damp mix isused and molded under pressure, as distinguished from the puddleprocess. Heretofore the puddle process has been considered to producearticles having the most desirable distribution of bond, grains andpores, but from a commercial standpoint it is less satisfactory becauseseveral days time is required for the drying of the article before itcan be burned, and the finished articles has to be dressed and cut toshape. In the use of a damp mix, the product has had less desirablecharacteristics, but the drying time is shortened to a period of a fewhours, and the article can be formed in the mold directly to the shapeand size desired, so that very little triming or dressing of the moldedarticle is necessary.

By the use of the present invention articles are produced by the dampmethod, which are superior to those which have heretofore been pro--duced, and without the loss of time incident to the puddle process andwith all of the advantages of the damp mix method.

' If an abrasive or ceramic article be closely ob served three things inthe structure of the article can be noticed. If, for instance, thearticle be an abrasive wheel, the abrasive grainscan be seen, thebond-which cements the abrasive grains together can be seen, and thepore space can be noticed. These three things can be very much moreclearly noticed if the article be impregnated with a synthetic resin sothat the resin fills the pore spaces, the wheel then baked to set theresin, and then polished.

When the article has been treated in this way, the surface shows- (1)The grains in cross-section,

(2) The bond, which can be readily distin guished from the resin whichfills the pore spaces by the contrast in color.

(3) The voids or pores can be discerned readily by reason of the resinwhich fills them and which contrasts in color from the grain and thebond.

An article made by previously known methods, when treated in thisfashion and examined, discloses numerous patches of small area over itsentire surface where the grains are very densely clustered and wherethere is a very sparse amount of bond and a very little area of visiblepore space. Other patches will be seen wherein the grains are sparselydistributed, as compared with the first described areas, and there is apredominance of bond or of pore space.

If this article be an abrasive article, this characteristicconglomeration' of cubical sections having a wide variation in thegrain, pore, and bond distribution, has a very noticeable effect, whichefiects have heretofore been recognized, but could not be avoided. Theabrasive grains, of course, perform the grinding operations. The bond.is ordinarily softer, and the pore space determines, with the size ofthe abrasive grains, the cutting characteristics of the bonded abrasivemass. In those portions of the abrasive article where there are denseclusters of grains, the wheel will be very hard. Where the grains arerelatively sparse, and there isa predominance of bond, the action is onewhere there is little cutting, but in which heat is generated by reasonof the friction between the bond and the material being abraded. Wherethe wheel structure has a predominance of pore space, the wheel is centthe arbor hole.

soft and the cutting action is quite different from where there is adense clustering of the grains.

If the abrasive article be a wheel, this variation in the character ofvery small portions of the entire mass shows itself in the character ofthe work done. If the work is rough work, such as finishing castings,such local irregularities show up as pits and irregular open sectionsand cause the wheel to vibrate objectionably. If the wheel is forprecision work, the work will show chatter marks and slightirregularities when closely examined, and which cannot be avoided. Ifthe article, instead of being an abrasive article, is a refractoryarticle, the non-uniformity of structure also has its effect.

While refractory articles are generally of a low porosity as contrastedwith a grinding wheel wherein a high porosity is desirable,non-uniformity of structure results in uneven strains under varyingtemperature conditions, which strains manifest themselves in a tendencyto rupture and crack.

Not only have articles made by the usual methods possessed thischaracteristic variation between difierent small portions in the samearea of the article, but the average distribution of grain and bond andpore space in one area of the article may differ widely from the averagein another relatively large section of the article. For instance, if thearticle he an abrasive wheel, and the wheel is put on a spindle which ismounted to turn very freely, one side of the wheel will invariably befound to be at least somewhat heavier than the other side. This has.been recognized by the industry, and relatively tute a large portion ofthe grinding art, in which extremely small tolerances for balance havebeen established, and some of these operations require wheels that arevery closely balanced without being corrected by the application ofmetal adja- The methods used before our invention produced a largeportion of wheels in which the condition of balance was such that theyhad to be rejected for .use in connection with those operationsrequiring wheels of small tolerances.

In the usual practice of forming articles of this nature, the abrasivegrains and the bonding material are very carefully mixed for a long timein agitating mixers so as to secure as complete uniformity in thedistribution of the bond as is and to avoid the condition referred towhich exists where pressure is applied to a thick mass of a mixture ofthis nature. We have found, however, that such a method of filling themold does not result in uniform distribution of the mix in-the mold. Theoperator cannot, by throwing the material into the mold with a scoop,absolutely distribute evenly the number of scoopfuls which go into anyone area; he-cannot rake the material around inthe mold to assure anabsolutely even distribution; and finally, he cannot tamp all areas tothe same extent and with the same degree of pressure. Moreover, thetamping of one area may tend to disturb the grains in the adjacentareas. It is for these reasons that the best recognized practice priorto the present invention results in a wheel or other article in whichthere is not only a great probability of an uneven distribution of thematerial in defierent large sections of the article, but also the verywide distribution of grains, bond and pore space-in adjacent small areasor patches of the article.

According to the present invention, a method and apparatus are providedaccording to which articles are produced wherein there is consistently amuch more uniform distribution of grains, bond and pore space indifferent large areas of the article and the uniform absence of widelydiffering distribution of bond, grains and pore space in adjacent smallpatches or areas of the article, with the result that the waste due tounbalance or non-uniformity is very materially reduced, the operation ofbalancing, in the case of wheels, is made much less difficult, and thegrinding characteristics are comparable to those obtained with anabsolute uniformity of pore space, bond and grain.

The invention may be understood by reference to the accompanyingdrawings, in which:

Figure 1 is a more or less schematic drawin showing one formof apparatusfor carrying out the invention;

Figure 2 shows more or less diagrammatically the method used incalculating the grain and pore distribution as applied to an abrasivewheel embodying the present invention;

Figure 3 is a view similar to Fig. 2 showing only part of a wheel, butin which the diagrammatic representation of the variation between grainand bond in different small areas is comparable to that obtaining ingood quality wheels made in accordance with the present generalpractice;

Figure 4 is merely a legend for the explanation of Figs. 2 and 3;

Figure 5 is a typical graph actually plotted against an abrasive wheelformed by a damp mix process in accordance with the best known.methodsprior to the present invention, showing the maxima and minimapercentages in grain distribution in diiferent small areas of a wheel;

Figure 6 is a similar view of another wheel showing a characteristiccurve;

Figure 7 is a corresponding typical curve for the grain distribution inan abrasive wheel made in accordance with the present invention; and 7Figures 8, 9 and 10 correspond to Figs. 5, 6, and '7, respectively,except that the curves are plotted on the pore distribution in differentsmall areas instead of the grain distribution.

Referring first to Fig. 1 of the drawings, 2 designates a turntablehaving a mold thereon. The moldillustrated is for forming a wheel, andhas a central post 4 for forming the opening at the center of the wheel,but it will be understood that the mold may be of any suitable orpreferred shape. At the top of the mold is a strikeoff ring 5.

Suspended above the mold is a riddle 6 carried by a frame I which isvibrated by any suitable driving means (not shown) at a uniform rate.The area of the riddle is preferably at least 25% larger than the areaof the mold. The riddle is provided with a lower screen 8, and there arealso preferably provided one or more screens 9 above the lower screen,although these may be dispensed with. The mesh size of the lower screen8 is preferably less than the mesh size of the upper screen. In theriddle which we prefer to use the meshes of the lowermost screen do notexceed five times the average diameter of the grains and preferably areapproximately four 'meshes coarser than the mix to be distributed.

, The height of the riddle above the mold is such that the distancebetween the lowermost screen and the bottom of the mold is about 18inches, but this distance can be varied. It is preferable, however, thatthe riddle shall not be so high that the falling grains will produce anyconsiderable impact when they fall into the mold.

In carrying out the invention, the grain and the bond are mixed in theusual manner in the proportions commonly used, and for a length of timecorresponding to the length of time now considered advisable, and untilthere has been obtained as good distribution of the grain and the bondas canbe obtained by the stirring and agitating of the mix. This mix isthen placed in the riddle, being distributed around in the riddle asevenly as possible, and while the riddle is vibrating. The operation ofthe riddle is of course to sift the mix down into the mold, and the mixfalls into the mold in clusters of only av few grains. While the mold-isbeing filled in this manner, it is preferably rotated on the turntableat a uniform speed. By reason of the fact that the riddle is preferably25% larger in diameter than the mold, the uniform filling of the mold isinsured. When the mold is filled to the top of the strike-off ring, theexcess mix is carefully removed, by removing the ring and leveling witha straight edge, the operation being done care-- fully so that the mixremaining in the mold is not disturbed or is not compressed at any pointand is of uniform thickness.

After the mold has been leveled off, the mix in the mold is consolidatedinto the finished article. This is done by pressure in a press having aplunger arranged for cooperation with the mold, and the pressingoperation may be done in the con-. ventional or any preferred manner.

By carrying out the process in this manner, the article has a uniformityof distribution of grain, bond and spore space which distinguishes it inappearance, particularly when impregnated with a resin and polished, ashereinbefore described, from articles'of a like nature made by otherprocesses. This quality is due to a number of things. The mix is sodeposited in the mold that it is uniformly distributed and thisuniform'distribution is not disturbed by subsequent operations. .Themaximum increments or clusters which fall into the mold are not inexcess of one cubic centimeter, and, if the mesh of the riddle bears therelation to the mesh of the grain above described, these increments orclusters will be smaller. than one cubic centimeter and contain only arelatively few grains as contrasted with a large mass oi many cubiccentimeters and containing many thousands of grains which is thrown intothe mold when even a very small scoop is used. The riddling action alsoserves to distribute the bond. over the grain, because in passingthrough the riddle excess bond is transferred from some of the. grainsonto other grains which may be deficient in the amount of bond clingingto them. This is by virtue of the rubbing action of the grain upon thewire produced by the screen of the riddle, causing the excess bondmaterial to be rubbed off one particle and deposited on others.

The uniform vibration of the screen severs at regular intervals thestreams of material passing through the screen and thus makes the massesor groups of grains falling into the mold of uniform length as well asof uniform area. These small portions or masses, as explained above,contain relatively fewgrains, and generally do not exceed 15 times thevolume of the coarsest grain in the mix. As stated above, the volumewould rarely exceed one cubic centimeter, and would.

ordinarily be considerably less than this.

The addition of particles to the mold'at uniform velocity is also ofimportance, and this is accomplished by suspending the vibrating screenat a definite height above the mold and vibrating it at a uniform speed.The small groups of grains thus .fall into the mold with substantiallyequal impact, and because of the relatively short distance the impact isrelatively slight.

Uniform distribution of'the mix over the mold is secured, and this isproduced by having the screen larger than the mold, by keeping thescreen covered with mix, and by rotating the mold while it is beingfilled. r I

By securing uniform distribution of the mix over the surface of themold, terracing of the mix, which results when it is piled up, isprevented. The step 01 filling the mold to excess and then striking offthe excess removes any possibility of there being irregularities in thedepth or thickness of the material in the mold. I

The advantages of the present method and apparatus are made more fullyapparent by the detailed inspection of the articles made bythe use ofthe present invention.

In articles made according to the present invention the differencebetween the average grain content of those areas in which the grainconcentration is a minimum, and the average grain content of those areasin which the grain concentration is a maximum is less than 60% of thegrain content of an area having a minimum grain concentration, whereasthe diiferences in articles made by processes heretofore known have been100% or greater. Likewise the pore distribution in articles made inaccordance with our invention is characteristically more uniform thanhas been obtainable by methods employed heretofore. The differencebetween the average pore space of those areas in which pore space is aminimum and the average pore space of those areas in which pore space isa maximum is less than 60% of the pore space of an area having a minimumpore space. On the other hand, the usual methods of manufacture haveresulted in articles in which the difference was 100% or Q cordance withthe best known prior art practice and of the same grain and'bondproportions and of the same grain size is likewise treated. Then theimpregnated surface of each wheel is ground and polished, ashereinbefore described. When the wheels have been thus treated .it iseasily possible for one familiar with abrasive wheels to scan thesurface and pick out small areas over the surface where the grains aremost densely arranged, and to'pick out other small areas where thegrains are least densely arranged.

The article under examination is ordinarily divided into a number ofareas of equal size. This is indicated in Figs. 2 and 3 where the radiallines divide the surface of the wheel into six segments. The operator,in examining a small wheel, picks one spot having the maximum grainconcentration in each segment. He also picks a small area having themaximum pore area in the same segment. This is done in each of the sixsegments, the areas marked off being the same size in each case. In theusual practice of making such comparisons, the average area of each spotchosen is that covered by not less than 50 nor more than 100 maximumsized grains of the grit of which the article is composed, and

they are ordinarily between one-quarter and onehalf inch square.

Since the number of areas required to give a fair and reasonable averageof the maxima and of the minima percentages of each constituent mustvary with the area of the wheel and also with the grit size of theabrasive grain used, we have found it desirable to determine the numberof observations to make from the formula N-f/ZE in which N is the numberof areas to be examined, A is the area in inches of the broadestsurfaceof the article, and G is the average mesh size of the abrasivegrain.

To illustrate this method let us assume that we wish to know how manyareas to measure in a wheel 30 inches in diameter composed of grainranging in size from those which will pass through a 58 and not througha 60 mesh to the linear inch screen to those which will pass through a28 mesh screen but which will not pass through a screen with 30 meshesto the linear inch. The area of a 30 inch diameter wheel is 707 squareinches and the average mesh size of the particles ranging from 30 to 60grit is 45. The number of observations to make, therefore, is

for each constituent viz. grain, bond and pore space.

In Figure 2 the small areas outlined and marked a are areas of maximumgrain concentration. Those areas marked b are areas in which there is apredominance of pore space. These areas are then examinedmicroscopically under a cross ruled ocular, and in each dense spotexamined the relative area occupied by grains is determined, and in eachporous spot the relative area occupied by grains is also determined.Likewise, in each dense spot the relative area of pore space iscalculated and in each porous spot the relative pore area is alsoobserved. In a similar manner, the relative areas occupied by bond ineach of the spots is determined. Average values for the grainconcentration in the dense spots can thus be calculated and averagevalues of the areas of the grains in the spots can be calculated.

In Figure 3 the same procedure is followed and the areas marked a areareas of maximum grain concentration, and the areas marked b are theareas of maximum pore space.

The results may be plotted. graphically. Figs.

5 and 6 are for the results on areas of maximum grain concentration inabrasive wheels made in accordance with the best known prior methods andconsidered to be of good quality,

whereas Fig. '7 is plotted against a typical wheel corresponding graphfor a typical wheel made ,1

in accordance with the present invention.

Taking Fig. 5, for example, the six.points plotted at the top representthe grain concentrations observed in the respective six areas examined.The dotted line marked Average" represents the average grain area forthe six points plotted. The lower graphin Fig. 5 shows the grainconcentration in the areas of minimum grain concentration, and thedotted line indicates the average. It will be seen that the two linesmarked Average for these two curves are separated by 22 Fig. 6 likewiseshows a similar curved plotted against another typical wheel of the bestprior art construction, the separation between the two lines markedAverage being even greater than in Fig. 5. It will be seen that thesecurves are very abrupt ones, jumping widely from one side of the averageline to the other. In Fig. 7 it will be noted that the maximum andminimum average lines are separated by less than 15% and that there isnot the wide fluctuation to each side of the average line that obtainsin Figs. 5 and 6. Because the average lines of Fig. 7 are much closertogether than the average lines of Figs. 5 and 6, Fig. 7 shows that awheel embodying the present invention has a much more uniformdistribution of grains than did the wheels on which the curves for Figs.5 and 6 were plotted.

The fact thatthe curves in Fig. 7 fluctuate less widely to oppositesides of the respective average lines, and that the average lines arecloser together, whereas in Figs. 5 and 6 there is a wide fluctuation ofeach curve to opposite sides of its average line and the average linesare widely separated, indicates that there is a much morein thedifierent small areas examined and also.

a separation'bf approximately 30% between the average line for themaximum and the average line for the minimum. In Fig. 10 the averagelines are very much closer together, being separated by about 15%.

As previously noted, an examination of Figs. 5 and 6 shows a very widefluctuation in the areas, examined from one side of the average line tothe other. In other words, the average lines are not only further apartthan they are in Fig. 7, but the graphs indicate much widerfluctuations. The same is true in Figs. 8 and 9 with respect to the poredistribution, while I0 shows very little variation to opposite sides ofthe average lines. An inspection of Figs. 7 and 10 shows that in mostcases the variation from one side of the average line to the other isless than 5 and the separation between the average lines is less than20.

In the illustrations given for normal objects in Figs. 5 and 6 and 8 and9, the average lines are spaced considerably further apart and indicatethat the variation in the small areas for both grain and pore spacesfluctuates more than to each side of the average line.

An article made in accordance with the present invention may be furthercharacterized in this way: That when the pore spaces of the arti- .cleare filled with a substance to make the pore spaces stand out incontrast to the grains and the surface of the article is then polished,the article has a uniformly stippled appearance subour invention and onemade by the prior art prac-' tice cannot be illustrated readily by thedrawings I but it can be detected readily in the wheels themselves byobservation.

The differences which have been pointed out above in connection with anarticle produced by practicing the method herein described and with theuse of the apparatus as herein disclosed, clearly show that by the useof the present invention, bonded abrasive articles may be produced whichare physically difierent from similar objects as produced 'at thepresent time by the generally accepted methods and with the generallyused apparatus. This physical and structural difference which iseffected in the articles through the use of the present invention,manitests itself in abrasive wheels, for instance, for precisiongrinding, for an abrasive wheel made in accordance with the presentinvention will produce work'which is noticeably more free of chattermarks than wheels which have heretofore been made.

That the method used is materially different from present methods isevidenced by the fact that in production work the number of rejections'of wheels because of their being out of balance overa long extendedrunof production has been less than 2%,-whereas it has been the experiencethat as high as 30%, and always considerably greater than 2%, of thewheels produced by the previously known methods for use in connectionwith grinding operations requiring close tolerances as to balance, havehad to bediscarded for out of balance exceeding the limits set.

scribed in pages 51 and 52 thereof) is disclosed by penetration tests.According to such a test six abrasive wheels made in accordance with thepresent invention and six made according to Searles method were burnedin the same kiln at the same time and under the same conditions oftemperature and atmosphere. The same bond was used and the same size ofabrasive was used and the abrasives in .both cases were of like quality.The kiln glaze was removed from the surfaces of the wheels after theywere fired, and the new surfaces were tested for hardness under the sameconditions and by the same methods. This test comprised subjecting thewheels at four places on each face to the impact action of a Thisdifference between the number of times, and then measuring the depth towhich the chisel penetrated the wheel. According to this method thedifference in the structure of two abrasive wheels, or the difference instructure of two areas in one abrasive wheel, are indicated by thedifference in the depth of penetration of the tool; the penetration intoan area where the granular material is sparse is greater than the degreeof penetration into an area where the grain concentration is themaximum. The results of these tests are given in the following table:

Ratio of maximum penetration to minimum penetration in each. wheel Byour method By Sear-1e 's method 110 to 100 135 to 100 116 to 100 138 to100 117 to 100 140 to 100 118 to 100 146 to 100 120 to 100 148 to 100This impact penetration test is a standard test used to determine therelative hardness of bonded abrasive articles. The above figures showthat wheels made by the Searle method are not as uniform as those madeby the present process, since the maximum penetration in a given wheelis from 35% to 48% greater than the minimum penetration in the samewheel; whereas the maximum penetration is only to great--' er than thepenetration in a wheel made in accordance with our invention. Thisillustrates that by using the same materials and subjecting them to thesame conditions, a wheel embodying the present invention has a physicalresistance to penetration that is substantially uniform over the surfaceof the wheel.

The methods of testing as herein described are the best available onesat present known to the abrasive art for determining the character of anabrasive structure. The method of dividing the object into a number ofsections and selecting in each section a space of maximum'grain and aspace of maximum pore distribution, and then calculating the areas bythe use of a cross ruled ocular is similar to the method well-known togeologists in the study and analysis of rock formferred apparatus, itwill be understood that changes and modifications may be made thereinand variations may be made in the procedure within the contemplation ofour invention and under the scope of the following claims.

We claim:

1. The method of making an article of uniform density from a mixofbonded grain which comprises adding the mix to a mold in small uniformlydistributed portions not exceeding substantially one cubic centimeter involume and then applying pressure to the material in the moldsimultaneously over the entire surface of the material and before anysmall areas have been individually tamped orcompacted.

2. The method of making an article of uniform density from a mix orgrains and bond which comprises adding the mix to the mold incentimeterin volume until the said mold is filled to excess, striking off from themold the excess mix above a predetermined plane, and then pressing themix in the mold.

3. The method of making an article of uniform density from a mix ofgrain and bonding material which comprises adding the mix to the mold insmall uniformly distributed portions not exceeding substantially onecubic centimeter in volume, removing the excess mix above apredetermined plane, and then pressing.

4. The method of making an article of uniform density from a mix ofgrains and a bond which comprises adding the mix to a mold in uniformlydistributed portions not substantially exceeding fifteen times thevolume of the coarsest grain, striking off the uniformly distributed mixto a predetermined upper limiting plane, and then pressing.

5. The method of making an article of uniform density from a damp mix ofgrains and bonding agent which comprises depositing the mix in the moldfrom a distributing device of the sifter or gyratory riddle typeoperated above the mold, and subsequently applying pressure to thecontents of the mold simultaneously over the entire surface of thematerial and before any small areas have been individually tamped orcompacted.

6. The method of making an article of uniform density from a damp mix ofgrains and bonding agent which comprises adding the mix to the mold insmall uniformly distributed portions not exceeding substantially onecubic centimeter in volume, simultaneously rotating the mold, andsubsequently pressing the contents of the mold.

'7. The method of making an article of uniform density from a mix ofgrains and bonding agent which comprises distributing the mix over anarea. greater than and including the mold from a device of the sifter orgyratory riddle type operated above the mold while simultaneouslyvrotating the mold, subsequently striking off the excess material fromthe mold, and pressing the material.

8. The method of producing an article of uniform density from a mix ofgrains and a bonding agent which comprises shaking the mix into a moldfrom a device of the sifter or vibrating riddle type operated above themold and having a screen whose meshes do not exceed five times theaverage diameter of the particles of grain in the mix, striking off theexcess mix from the mold, and pressing.

9. The method of producing an article of uniform density from a mix ofgrains and a bond which comprises shaking the mix from a device of thesifter or vibrating riddle type into a rotating mold, striking off theexcess material from the mold, and pressing.

10. The method of producing an article of uniform density from a mix ofgrains and a bonding agent which comprises shaking the mix 'through ascreen whose mesh is less than five times the average diameter of theparticles of grain in the mix into a mold, striking ofi any excess mixfrom the mold, and pressing the mix in the mold.

11. The method of making an article of substantially uniform densityfrom a mix of grains and a bond which comprises the steps of adding themix to the mold in small uniformly distributed portions and at asubstantially uniform velocity, striking off excess mix from the mold,and pressing.

12. Apparatus for the manufacture of bonded articles comprising a riddlehaving a screen, the mesh of the screen not exceeding five times thediameter of the average particles of grain to be passed therethrough,and a mold spaced below the screen of the riddle to receive screenedmaterial directly, the area of the riddle exceeding the area of themold. I

13. Apparatus for producing an article of uniform density comprising arotatable mold, and a riddle spaced above the mold whose area exceedsthe area of the mold, said riddle having a screen therein, the mesh ofwhich does not exceed five times the average diameter of the particleswhich pass through the riddle into the mold.

14. The method of making an article of uniform density from a mix ofgrains and bond which comprises shaking the mix uniformly from auniformly vibrated riddle into a mold while maintaining a substantiallyeven distribution of material in the riddle, striking off excessmaterialfrom the mold, and pressing.

15. The method of making an article of uniform density which consists incontinuously adding to the mold small particles of mix, said particlesbeing added uniformly across the mold until it is filled to provide inthe mold a substantially uniform layer, and consolidating the mix.

16. The method of making an article of uniform density which consists incontinuously adding to the mold small particles of mix, said particlesbeing added uniformly across the mold until it is filled to apredetermined upper limiting plane, and consolidating the mix, theparticles being added to the mold at a substantially uniform velocity.

17. The method of forming an article from a damp mix comprising grainsand a bond, which comprises gradually filling an empty mold form to adesireddepth of fullness with the mixture by adding the mixture in smallincrements of a relatively few grains and not exceeding a cubiccentimeter in volume, and maintaining the depth to which the mold isfilled uniform throughout its area, and allowing such small incrementsto settle normally, and then applying pressure to the material in themold simultaneously over the entire surface of the material and beforeany small areas have been individually tamped or compacted.

18. The method of making an article of uniform density from a mix ofbonded grain which comprises adding the mix to a mold in small uniformlydistributed portions not exceeding one cubic centimeter. in volume,striking off excess material to leave a fiat uniformly distributed layerdefined by upper and lower substantially parallel surfaces and thenapplying pressure to the contents of the mold.

19. The method of making an article of uniform density from a mix ofbonded grain which comprises adding the mix to a fiat bottom mold insmall uniformly distributed portions of comparatively uniform size andnot exceeding one cubic centimeter in volume, striking off excess on afiat bottom from a device of the sifter or vibratory riddle typeoperated above the mold, striking off the deposited miX to asubstantially uniform depth and then pressing.

21. The method of making an article of uniform density from a mix ofbonded grain which comprises depositing the mix in a mold cavity from adevice ofthe sifter or vibrating riddle type operated above the moldcavity, striking of! excess mix, and pressing the contents of the moldbetween substantially parallel flat surfaces.

RAYMOND C. BENNER. PRESCOTT H. WALKER. WILLIAM G. SOLEY.

